The use of a high-gradient magnetic field to separate magnetically attractable particles from a fluid in which they are suspended is well known. Moreover, magnetic separation devices are used in a variety of industries including pharmaceutical, medical, agricultural, scientific and engineering fields. For example in biotechnology, a high-gradient magnetic field may be used to separate magnetically labeled bone marrow cells from a blood sample.
WO 90/14891 DYNAL A.S. discloses a conventional magnetic separation device whereby a test-tube/sample vessel, containing a fluid in which magnetically labeled particles are suspended, is arranged adjacent a strong magnet. The labeled particles are magnetically attracted to the side of the test-tube nearest the magnet. Thus, the supernatant is easily removable from the test-tube using a pipette whilst the magnetically labeled particles are left in the tube.
In order to save time, it is often desirable to process a large number of samples at once using a linear rack-like arrangement or tray-like arrangement. For example, the magnetic separating device disclosed in WO 90/14891 DYNAL A.S. comprises a rack for supporting a plurality of specimen containers. At least one magnet is arranged adjacent the rear portion of each test-tube such that the magnetic particles are attracted and adhere to the inside surface of the test-tube nearest the magnet; i.e. the interior surface at the rear of the sample vessel.
U.S. Pat. No. 4,896,560 GEN PROBE INC also discloses a magnetic separation rack where only one magnet is arranged immediately adjacent each test-tube. In this case, the magnet is arranged to one side of the test-tube and at an upper portion thereof.
It has been found that the separation of magnetically labeled particles is somewhat limited and restricted by the use of magnets on only one side of a test-tube. Moreover, the separation of magnetically labeled particles from a fluid is unsatisfactory if only a portion of the sample is subject to a magnetic field.
Whilst a rack-like arrangement is convenient for simultaneously processing a large number of samples, it is well known that the visual inspection of a sample vessel placed within a rack-like arrangement is imperfect. Some effort has been made to overcome this problem. For example, WO 90/14891 DYNAL A.S. provides a transparent plate so that an upper part of the test-tube is more clearly visible. Nevertheless, a lower portion of the test-tube is still hidden from view.
A magnetic separation rack comprises multiple chambers to receive test-tubes/sample vessels. The chambers are configured to have a predetermined diameter and depth. Obviously, the magnetic separation rack may only receive test-tubes having a diameter less than the diameter of the chamber. Thus, a magnetic separation rack is often restricted to processing samples in test-tubes of a particular range of diameters. Moreover, a sample vessel placed within a magnetic separation rack that is shorter in length than the depth of the chamber will be difficult to retrieve from the chamber and a sample vessel placed within a magnetic separation rack that is substantially longer in length than the depth of the chamber may mean that only a part of the sample is subject to a magnetic field.
Accordingly, there is a need to provide a magnetic separation device that can alleviate and/or overcome at least some of the above-mentioned problems. More specifically, the invention seeks to provide a magnetic separation rack that is suitable for processing a plurality of samples in an array. The invention seeks to provide a magnetic separation rack that can separate magnetically labeled particles more efficiently than the prior art. The present invention seeks to provide a magnetic separation device wherein a sample vessel mounted in the device is visible so that the inspection of the sample is easier than the prior art. The present invention also seeks to provide a magnetic separation device that is suitable for receiving different size sample vessels.